The sister of alleged murder victim Philip James Nisbet broke down in tears when she saw the handwritten signature on a suicide note had vanished, a court has heard.

Lee-Anne Cartier made the discovery when she met the coroner in November 2010 shortly before an inquest into her brother's death.

She believed the handwritten signature "Phil" on the bottom of a suicide note she had seen after he died was fake and had brought evidence – birthday cards with his signature on them – to prove it.

"How the hell could she [murder accused and Nisbet's widow Helen Milner] do this?" she recalled saying at the time.

"This isn't it [the suicide note she saw]."

Cartier told the jury the content of the note had also changed.

"It [the second note] is a wee bit more soppy," she said.

The evidence emerged during the fourth day of the murder trial, which is set down for three weeks in the High Court in Christchurch.

Milner, 50, is on trial for the murder and attempted murder of Nisbet, 47, her husband, at their Checketts Ave home in Halswell.

The Crown alleges Milner drugged him by mixing Phenergan with his food and then may have suffocated him while he was sedated.

Cartier, formerly from Queensland, said she first heard about a suicide note when Milner phoned her within days of her brother's death.

Milner read it to her and said she found it in a locked safe after working out the combination.

The note said Nisbet's son, Ben Porter, was not his biological son and he could not face him again.

Milner told her she would have a DNA test done to see if it was true, with funeral director Glen Rossiter-Campbell apparently able to get one done cheap.

At the same time she told Cartier about documents she said she had found in Nisbet's briefcase. They allegedly included a little black book that showed he had been having affairs, and an instruction book on how to be a male prostitute.

"I was shocked, because Phil wasn't that sort of guy," Cartier told the jury.

"He was more of a shy person. He wouldn't be able to lie and get away with it."

Cartier first saw the typed suicide note with "Phil" handwritten at the bottom about five weeks after her brother's death.

She had flown to New Zealand for her son's 21st birthday and was staying with Milner at her Checketts Ave home.

Barry Hayton was there and sleeping in the same bedroom as the accused killer, Cartier said.

The suicide note was consistent with what Milner read to her on the phone, but she did not recognise the signature as her brother's.

She was with her son, Lance Connelly, when he was shown the same note a few days later, she said.

Cartier also approached Rossiter-Campbell about the DNA test Milner had talked to her about. He denied any knowledge of it.

"He was very, very angry. He said: 'that would destroy my career'."

SUICIDE 'COMPLETELY OUT OF CHARACTER'

Alleged murder victim Philip James Nisbet was not depressed in the lead up to his death and unlikely to have been suicidal, a court has heard.

The Crown has alleged that Milner made two attempts on her husband's life on April 15, 2009, using the anti-allergy and sedative drug Phenergan.